1. Field of the Invention
The present invention relates to a plug structure for connecting a pair of lead wires comprising a signal wire and a ground wire to an apparatus such as an audio apparatus.
2. Description of the Related Art
In an apparatus employing a lead wire for wiring, for example, an audio apparatus, an amplifier and a speaker are connected to each other by a pair of lead wires comprising a signal wire and a ground wire. Connection between a lead wire and such an apparatus is usually established as follows. As shown in FIG. 11, a lead wire is, at its skinned end, connected to a connector, called a lever terminal 103, attached to a terminal plate 101 provided on the back-surface side of the apparatus.
That is, a lever 105 is rotated in a clockwise direction viewing the figure against a force of a torsion spring 107, and a skinned end of a lead wire 109 is inserted into an insertion hole 111 of the lever terminal 103. Upon a return of the lever 105 to its original position, the lead wire 109 is caught in between a metal contactor 113, which is formed integrally with the lever 105, and a metal contactor 117 formed inside a housing 115 of the lever terminal 103, and is thereby connected to the metal contactor 117.
However, modem audio apparatuses, in contrast to conventional ones having a 2-channel system, have come to have a 4- or 6-channel system, i.e. require a larger number of speakers. This requires that the lead wire 109, formed by using a signal and a ground wire in combination, be separately connected to each of the speakers. Consequently, as shown in FIG. 12, the terminal plate 101 on the back-surface side of the amplifier is provided with a multiplicity of lever terminals 103 arranged in line.
Workers find difficulty in performing connection operations in the terminal plate 101 on the back surface of the amplifier, because the visibility of the work area is poor from the worker position. It is also extremely difficult to connect a multiplicity of lead wires 109 to their respective lever terminals 103 without fail.
Due to the difficulty of the connection operations, the lead wire 109 cannot be connected to the terminal with its skinned portions kept in a deeply-inserted state. Consequently, adjacent portions are brought into contact with each other, causing short circuits. Moreover, due to the poor visibility of the work area, the signal and ground wires, although they are usually distinguished from each other by their skin colors (red and black), might be inadvertently connected to reverse positions.
To overcome such inconveniences, a connection method as shown in FIG. 13 has been proposed that employs a plug 125. Specifically, a signal wire 121 and a ground wire 123, used in pairs as a lead wire 109, are attached to the plug 125, and this plug 125 is inserted into a socket 127 provided on an amplifier side.
That is, the end of each of the lead wires 121 and 123 is fixed in advance to its respective metal-made connector terminal 129. The connector terminal 129 is barrel-shaped, and its rear-end portion (left-end portion viewing the figure) has a U-shaped section. Upon insertion of the skinned end of the lead wire 109, the barrel is subjected to caulking, thereby fixing the lead wire 109 to the connector terminal 129. The connector terminal 129 has its substantially cylindrical front-end portion formed as a contact terminal 133, into which a pin terminal acting as an amplifier-side terminal 131 is inserted so as to be in contact therewith. These two connector terminals 129 with the lead wires 109 fixed thereto are received in their respective housing portions 135 formed in a single plug 125 so as to be retained.
Formed in a terminal plate 137 disposed on the back surface of the amplifier is a connection recess 139 constituting the socket 127 which is engaged with the plugs 125. Two apparatus-side terminals, or pin terminals 131, are formed inside the connection recess 139 protruding therein, these corresponding to the signal wire 121 and the ground wire 123, respectively.
To prevent the plug 125 from being inserted in a 180-degree inverted position, the connection recess 139 has a rib 141 formed on its inner side along the insertion direction so as to be protruded, and the plug 125 has, on its outer surface, a groove 143 which receives the rib 141. The plug 125 and its corresponding socket 127 have the same skin color.
In the connector shown in FIG. 13,
(1) By providing the concave groove 143 and the rib 141 for the plug 125 and the socket 127, respectively, the plug 125 can be inserted in a proper position, thereby preventing the signal and ground wires from being connected in reversed polarity.
(2) By giving the plug 125 and its respective socket 127 the same skin color, the lead wire 109 can be connected to the speakers for a multi-channel system with no possibility of wrong wiring.
(3) Since the skinned portion of the lead wire 109 is not exposed, adjacent lead wires 109 do not make contact with each other. Consequently, short circuits can be prevented.
(4) In this connector, unlike the lever terminal 103 shown in FIG. 111 which requires two operations: rotation of the lever 105; and insertion of the lead wire 109, the connection operation can be completed simply by inserting the plug 125. Therefore, even though the back surface of the amplifier is not exposed to the worker view, the connection operation can be easily achieved with one hand.
However, the connector shown in FIG. 13 lacks versatility. For example, in a case where an audio enthusiast tries to connect a specially-designed thick lead wire to the speaker, whereas the lever terminal 103 shown in FIG. 11 conforms to such a requirement, the connector in question is unusable. That is, only the lead wire 109 attached in advance to the plug 125 may be acceptable.
To achieve both of the convenience of the plug 125 shown in FIG. 13 and the versatility of the lever terminal 103 shown in FIG. 11, two types of connectors, i.e. the socket 127 and the lever terminal 103, need to be provided in a single back-surface panel of an amplifier or the like. This leads to an undesirable increase in the number of constituent components, causing space shortage in the back-surface panel.
The above description deals only with problems associated with connection between an amplifier and a lead wire provided in a speaker. However, similar problems tend to occur when a lead wire, realized by using a signal and a ground wire in combination, is connected between another device constituting an acoustic or other apparatus.
The present invention solves the above-described problems, and accordingly its object is to provide a plug that prevents reverse insertion of a signal and a ground wire arranged in pairs, prevents occurrence of short circuits in adjacent lead wires, facilitates connection of the lead wires, and allows connection of lead wires of any other type, i.e. offers versatility.
To achieve the above object, according to a first aspect of the present invention, a plug for connecting a pair of lead wire comprising a first lead wire and a second lead wire to an apparatus, comprising:
a plug housing configured so as to be insertable into and withdrawable from a connection recess provided on an apparatus side;
a pair of plug-side contact terminals disposed inside the plug housing, the plug-side contact terminals being contacted by a pair of apparatus-side terminals corresponding to the first and second lead wires;
reverse insertion preventive means for providing the plug housing with an asymmetrical profile so that it is inserted into and withdrawn from the asymmetrically-configured connection recess only in a predetermined position; and
connecting means for connecting a pair of plug-side contact terminals to the first and second lead wires, respectively,
the connecting means being clamp means detachably attached to the first or second lead wires.
Being configured so as to be insertable into and withdrawable from the connection recess on the apparatus side and provided with the reverse insertion preventive means, the plug housing can be engaged with and connected to an apparatus-side socket, which is engaged with and connected to the plug with the lead wire attached thereto, the lead wire being, at its end, fixed to a connector terminal.
Being formed as clamp means, the connecting means is capable of connecting a lead wire of an arbitrary thickness to the plug-side contact terminal.
According to a second aspect of the present invention, in the plug according to the first aspect, the pair of lead wires are connected between an amplifier and a speaker in an audio apparatus. A socket provided in the amplifier or speaker constitutes the connection recess. The reverse insertion preventive means is composed of a recess and a projection fitted into the recess, the recess is formed in one of the connection recess and the plug housing and the projection is formed in the other of the connection recess and the plug housing.
It is possible to use a pair of lead wires of an arbitrary thickness for connection between the amplifier and the speaker.
The reverse insertion preventive means allows the plug to be inserted into the connection recess only in such a state that the recess and the projection are engaged with each other, thereby preventing the amplifier and the speaker from being connected to each other in reversed polarity.
According to a third aspect of the present invention, in the plug according to the first or second aspect, the clamp means comprises:
a plate spring formed integrally with the plug-side contact terminal; and
a rotary lever rotatably supported by the plug housing, the rotary lever pressing the plate spring so that when the first or second lead wires are inserted into the plug housing, they will be clamped between the plate spring and the inner wall of the plug housing.
As the rotary lever is rotated, the plate spring is pressed, whereby the first or second lead wires are clamped between the plate spring and the inner wall of the plug housing, and is thereby electrically connected to the plug-side contact terminal which is integrally formed with the plate spring.
By rotating the rotary lever in a reverse direction, the pressure on the plate spring is released, whereby the first or second lead wires are unclamped and thus can be pulled out.
According to a fourth aspect of the present invention, the plug according to the third aspect further comprises:
a pressing pawl disposed in the rotary lever for applying a pressing force; and
a pressing recess formed in a portion of the plate spring at which pressing force is applied,
wherein the pressing pawl crosses over the pressing recess only when the rotary lever is rotated into an unclamped state.
In the clamped state, the pressing recess is pressed by the pressing pawl, whereby the rotary lever is settled in a rotation position to achieve clamping. Moreover, since the rotary lever is inhibited from rotating until the press pawl crosses over the pressing recess, it never occurs that the rotary lever is rotated into an unclamped state by an inadvertent external force.
According to a fifth aspect of the present invention, in the plug according to the first or second aspects, the clamp means comprises:
a plate spring formed integrally with the plug-side contact terminal; and
a rotary lever rotatably supported by the plug housing, the rotary lever allowing the first or second lead wire, inserted into the plug housing, to be gripped and clamped between the plate spring and the plug housing.
As the rotary lever is rotated, the first or second lead wire is clamped between the plate spring and the inner wall of the plug housing, and is thereby electrically connected to the plug-side contact terminal which is formed integrally with the plate spring.
By rotating the rotary lever in a reverse direction, the first or second lead wire is unclamped and thus can be pulled out.
According to a sixth aspect of the present invention, in the plug according to the fifth aspect, the rotary lever is provided with an engagement portion. The rotary lever is, at its engagement portion, fitted into the plug housing when set in a rotation position so as for the first or second lead wire to be gripped between the plate spring and the plug housing, thus attaining a clamped state.
The rotary lever is engaged with the plug housing in a rotation position for achieving clamping, and is thus prevented from being rotated into an unclamped state by an inadvertent external force.
According to a seventh aspect of the present invention, in the plug according to the fifth or sixth aspect, a pair of clamp means have an integrally-formed rotary lever, in which by the rotation of the rotary lever, the first and second lead wires are clamped or unclamped concurrently.
The first and second lead wires can be concurrently clamped or unclamped by the rotation of the rotary lever.
According to an eighth aspect of the present invention, in the plug according to the first or second aspect, the clamp means comprises:
a contact plate formed integrally with the plug-side contact terminal;
a plate spring arranged opposite to the contact plate, the plate spring being loaded with a force that tends to move it toward the contact plate so as for the first or second lead wire to be gripped and clamped between the contact plate and the plate spring; and
a push button for achieving unclamping by pressing the plate spring in a direction reverse to a force-loading direction.
The first or second lead wire is gripped between the contact plate and the plate spring which is loaded with a force that tends to move it toward the contact plate, and is thereby electrically connected to the plug-side contact terminal. When the push button is pressed, the plate spring is moved away from the contact plate, whereby the first or second led wire is unclamped and thus can be pulled out.
According to a ninth aspect of the present invention, in the plug according to the first or second aspect, the clamp means comprises:
a contact plate formed integrally with the plug-side contact terminal;
a pressing member arranged opposite to the contact plate, the pressing member allowing the first or second lead wire to be gripped and clamped between the contact plate and the pressing member;
elastic means for loading the pressing member with a force that tends to move it toward the contact plate; and
a push button for achieving unclamping by pressing the pressing member in a direction reverse to a force-loading direction.
The first or second lead wire is gripped between the contact plate and the pressing member which is loaded by the elastic means with a force that tends to move it toward the contact plate, and is thereby electrically connected to the plug-side contact terminal. When the push button is pressed, the pressing member is moved away from the contact plate, whereby the first or second led wire is unclamped and thus can be pulled out.
According to a tenth aspect of the present invention, in the plug according to the ninth aspect, the contact plate, the pressing member, and the push button are each arranged in pairs corresponding to each of the first and second lead wires. Of these components, the pressing members and the push buttons are each disposed at both ends of an U-shaped member serving as the elastic means.
The elastic means is realized as an U-shaped member and thus serves also as a paired clamp means.
A pair of push buttons are grippingly pressed to unclamp the first and second lead wires concurrently.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.